1. Field of the Invention
The invention relates to a method and a device providing a safety system for roller blinds, sun awnings, gates and the like.
2. Description of the Related Art
It is known that the actuating systems for roller blinds, to which reference will be made by way of example although the invention is also applicable to other movable barriers, are provided with safety devices for detecting when the roller blind, during its movement—especially its downwards movement—strikes an obstacle. After making impact, normally the roller blind is driven so as to reverse its direction of travel.
Many solutions of this type are known. In particular, a subassembly of such solutions makes use of a mechanical play existing between the drive shaft of the actuating system and the roller onto which the roller blind is wound. EP 0,552,459 describes an actuating system in which play is provided between two teeth projecting from the casing of the motor (of the actuating system) and a bar perpendicular to a rod fixed to the wall, which rod supports the entire actuating system. The bar is provided with deformation sensors for detecting the deformation thereof and therefore, indirectly, the load acting on the motor, from which data for controlling it is obtained.
EP 0,497,711 describes an actuating system in which a free wheel is arranged between the shaft and the roller. Two concentric members in the free wheel have, associated with them, means which act so that the relative movement of these two members when the free wheel starts to function after the roller blind strikes an obstacle causes, by means of a switch arranged in the electric power supply circuit of the motor, the automatic reversal of the direction of rotation of the roller and the immediate upward movement again of the roller blind.
FR 2,721,62 describes an actuating system where the roller is connected to a sensor, the signal of which representing the angular speed of the roller—here as below relative to the stationary part of the actuating system which is fixed to the wall—is processed by a logic unit in order to produce a stopped condition for the motor of the roller blind. A free wheel is provided, arranged between the motor and the roller, and zeroes the speed of the roller when it strikes an obstacle.
DE 196 10 877 describes a control system for an actuating system of roller blinds, comprising a pressure bar (Druckbalken). This bar is activated upon rotation of the motor which actuates the roller blind and, by means of the pressure sensors in contact with the bar, a signal is obtained and used to control the actuating system. In particular, this signal is used to detect an obstacle encountered by the roller blind.
DE 197 06 209 describes a system for measuring variations in weight acting on a roller which carries a roller blind, depending on which a motor-driven actuating system (of the roller blind) is controlled and in particular is stopped. In order to achieve this result a sensor in the form of a mechanical switching component is used, said component comprising two parts which co-operate and the relative angular position of which (along a same axis) is variable. When the roller blind reaches the end-of-travel stop or an obstacle, the relative rotation of the two parts changes and may be detected by mechanical switches so as to perform control of the actuating system.
U.S. Pat. No. 6,215,265 describes a system for controlling a motor-driven actuating system for a roller blind which measures the torque of the motor and stops it when it exceeds a fixed maximum torque value or following a maximum variation in the torque per unit of time. In addition, the speed of the roller is measured and the motor is stopped below a predefined speed value (which can be obtained from a stored profile). A further characteristic feature is to leave rotational play between the roller and the shaft of the motor, so as to make use of it as a further way of deactivating the motor. No further information is provided in this connection.
DE 44 45 978 relates to a safety device for roller blinds in which the stationary part of the actuating system is fixed with a certain degree of play, allowing a limited angular movement about the axis of the shaft (onto which the roller blind is wound) and in which at least one pivoting interrupt lever with an associated spring is provided. During a dangerous event the spring pulls the lever against a switch so as to produce a malfunction signal.
All these solutions have drawbacks.
The solutions which, in order to detect the presence of an obstacle, control the consumption or the load of the motor must necessarily rely upon a variation in the consumption or load produced by the obstacle. This variation, in order to activate a protection system, must exceed a minimum activation threshold below which it is still possible for dangerous impact situations to occur. Moreover, since the controlled (or monitored) component is the motor of the actuating system, the component which actually causes the impact, namely the roller blind, which sometimes has considerable dimensions, is not monitored. It is particularly difficult to control the motors which are fitted to roller blinds such as shutters, Venetian blinds or external roller shutters which have a “bellows” structure where the variation in load following an impact with an obstacle is difficult to predict because it depends on the obstacle itself and the impact conditions. In fact, it is the deformation of the roller blind during impact which produces the variation in the load on the motor. Moreover, since it is dependent upon the characteristics of the motor, each system must be set for the specific application, which varies greatly depending on whether it is required to operate shutters, awnings, blinds, doors or entranceways which have a varying size, weight and characteristics.
With the solutions which instead make use of mechanical play between the roller and motor, a degree of uncertainty may arise during their operation. When the play is used to obtain protection by means of a slider travelling along the entire length thereof in order to activate a switch or similar solutions, necessarily the play must be gauged in relation to the particular application. Too small a play may trigger protection without an obstacle actually being present, since the roller blind may encounter along its path not an insignificant amount of resistance, such as that produced by dust which has accumulated (especially with time) or ice formations, or may simply encounter more friction than predicted, usually as a result of an increase in dimensions due to variations in temperature which may even occur on a daily basis.
Too great a play may trigger the protection when the entire weight of the roller blind is already acting on the obstacle, which is very dangerous if, for example, the obstacle is a person.
It is therefore easy to appreciate the difficulty of designing a reliable system which has acceptable operating margins and at the same time can be used in more than one application, in order to reduce the re-designing and adaptation costs.
If the mechanical play is associated with control of the roller speed, here too the already mentioned problems exist of having to choose the degree of play with a compromise between efficiency and the possibility of standardisation. Where, however, there is only control of the angular speed of the roller, whether or not a free wheel is used on the roller, the risks exists that this speed may fall and trigger activation only when the roller blind is already bearing dangerously on the obstacle, something which is all the more likely where the roller blind has a fold-up structure (for example a blind with several horizontal slats) since the edge of the roller blind subject to impact disengages from the roller.
Where, instead, mechanical play is used to monitor indirectly the parameters of the motor, the general performance of the actuating system suffers from the drawbacks of the systems where only the parameters of the motor itself are monitored. In this case the mechanical play is nothing other than an alternative sensor for an electrical or physical characteristic of the motor.